In the simplest case, the diffusion coefficient of the process is
inferred via assuming two-dimensional Brownian motion and plotting the mean square displacements of one or more identical protein molecules against time, then calculating the diffusion constant (D) from the slope of the resulting straight line (D = slope / 4). The resulting D value is inversely proportional to the frictional drag of the molecule against the membrane, and thus provides information about the membrane contacts and oligomer number of the molecule as it executes simple Brownian diffusion on a homogeneous membrane surface [1]}, [2]}, [3]}, [4]}. However, in more complex systems, Brownian motion can be inadequate for modeling
a protein with multiple diffusive states, since the protein may switch between different membrane docking geometries, or may undergo transient binding interactions with other membrane proteins, cytoskeletal elements, or membrane inhomogeneities [2]}, [4]}, [3]}, [8]}, [9]}, [10]}, [11]}, [12]}, [13]}, [14]}, [3]}, [16]}, [17]}, [18]}, [19]}. The resulting deviations of diffusive behavior from simple Brownian motion invite
a deeper interpretation of the underlying dynamics of the system.
